Non-intrusive thermal power monitor and method

ABSTRACT

A non-intrusive thermal power monitor and method for determining the amount of sensible heat withdrawn from or added to a fluid stream flowing in a conduit by an unknown source includes a thermal power transfer device that supplies or removes a known amount of heat energy to the fluid in a conduit. First and second temperature sensors sense the temperature of the fluid stream across the thermal power transfer device, and this information is used to determine a heat capacity rate of the fluid in the fluid stream. Additional non-intrusive temperature sensors sense the temperature of the fluid stream as it passes through and across a thermal power sink or heat source and provides a temperature differential. These temperatures are processed in a control circuit, and the thermal power added to or extracted from the fluid stream is determined in the control circuit by multiplying the measured temperature differential by the heat capacity rate of the fluid stream.

BACKGROUND OF THE INVENTION

This invention relates to an apparatus and method for monitoring theamount of thermal power added to or withdrawn from a moving fluidstream, and more specifically, to a non-intrusive apparatus and methodwhich measures the amount of thermal power input or extraction from aflowing fluid by determining the sensible heat capacity rate of thefluid and a temperature differential resulting from the thermal powerinput or extraction.

There has long been an interest in determining rapidly, economically andeasily the thermal power contribution to a flowing stream of fluid froman unknown source, or the thermal power extraction from the fluid streamby an unknown thermal power sink. A myriad of industrial and residentialsystems employ flowing fluid to which thermal power is either added ortaken away. It is quite useful to know the amount of that thermal poweradded to or extracted from the fluid for determining systemefficiencies, losses and capabilities. Thermal energy, which is thermalpower multiplied by time, may be considered of more fundamentalinterest; thermal power and thermal energy are related through the timeparameter and can readily be derived from each other.

There are various types of devices used for determining thermal powerinput into a fluid stream. These devices have tended to be relativelyexpensive and for that reason are of limited utility.

These prior art devices include intrusive systems. One such system is anull system. In the null system, temperatures upstream and downstreamfrom the unknown source of energy are taken. A heater supplies energyinto the stream and the temperatures upstream and downstream of theheater are taken. The energy input of the heater is adjustable to varythe temperature difference upstream and downstream of the heater toequal the temperature difference across the unknown source. When thesetwo temperature differences are the same, the amount of thermal energyintroduced into the stream by the heater equals the energy introducedinto the system from the unknown source. A null system is comparativelyexpensive. Null systems also can use too much energy; for example, whenthe temperature difference across the unknown source is high, a largeamount of energy is required to produce the same temperaturedifferential across the heater. Also, when the flow rate is high, alarge amount of energy may also be required from the heater to achievethe same temperature differential across the heater. Null systems mayalso require considerable peak power capacity to enable them to monitortransients, such as a blowdown of a hot storage tank. The large powerrequirements of a null system can require an intrusive heater, one thatis physically in the stream being monitored and not outside the stream'sconduit. Null systems can result in or necessitate undesirablealterations in the stream being monitored and complicating procedures.For example, when a large amount of heat energy must be introduced intothe stream, it may be necessary to cool the stream to prevent boiling.With high energy input, if heat input is not carefully controlled, thefluid could change state and boil. Further, cooling and then heating thestream results in considerable heat utilization. Null systems alsorequire continual adjustments resulting in complex electronics.

One specific form of null system is disclosed in U.S. Pat. No. 2,398,606to C. C. Wang, which is specifically designed for ultra-high frequencypower measurement. In this particular system, constant temperatureratios are imperative for accuracy.

Intrusive systems, such as the null system, require breaking into theline carrying the fluids. Breaking into the line is clearly adisadvantage.

Heat meters are also in the prior art. One representative of heat meteris described in U.S. Pat. No. 3,167,957 to Ziviani in which heattransferred from a fluid is measured. In Ziviani, an intrusive by-passduct removes a constant fraction of the fluid from a main stream. Thisconstant fraction is heated in the by-pass duct to a temperature that isa specified function of the amount of heat removed from the fluid in theoverall system. The Ziviani patent relies on a flow rate restriction inthe main stream which could result in scale build-up in a relativelyshort period of time.

There are substantial problems with heat meters of this type. A majorproblem is the necessity to divert fluid and to heat the diverted fluidin proportion to the amount of heat withdrawn by the overall system. Itis also exceedingly difficult to obtain a constant fraction of a fluid.In addition, devices of this type use thermocouples which are inherentlynon-linear. Systems of this type are intrusive because temperaturesensors are in the fluid and the by-pass duct must be connected to themain stream for diversion of that stream.

Another heat measuring device is taught in U.S. Pat. No. 2,931,222 toNoldge et al. A fraction of a fluid previously cooled in a heatexchanger is heated to its original temperature. With knowledge of thefraction, the specific heat of the fluid, and the temperature increase,the amount of heat energy taken from the fluid is readily determined.This device is similar to a null system except that it operates inreverse and only on a fraction of the fluid. The system has manydisadvantages including the fact that the inlet temperature of the fluidmust be known. Further, systems of this type to be accurate must avoidcorrosion or scale build-up, and fluid properties, such as viscosity anddensity, and flow rate, must remain the same; thus, if the viscosity orthe flow rate of the fluid changes, the system becomes inaccurate.

U.S. Pat. No. 3,802,264 to Poppendiek et al discloses a meter todetermine the flow rate of a stream and utilizes a heater to heat thefluid stream and measures the stream temperature increase. Temperaturesare not measured at or beyond the upstream and downstream ends of thepower input, but rather intermediate the ends of the power input. Inother words, the system of this patent monitors temperature before theheat is uniformly distributed throughout the fluid. With the temperatureincrease and the power input, the flow rate allegedly can be determined.

Thermally operated flow meters of the type taught in Poppendiek et alare necessarily restricted to laminar flow operation in order tomaintain required linearity. Further, the fluid must be homogeneous andit is necessary to know or to be able to derive the specific heat of thefluid. Also, other properties of the fluid, such as density, viscosityand thermal conduction, significantly affect the accuracy, necessitatingcalibration for each fluid type and input temperature. Consequently,such devices are rather limited in use and in application.

Hot wire anemometry is still another approach for measuring fluid flow.Here, a wire in the stream has power supplied to it. Heat from the wiretransfers to the stream. The rate at which heat is lost from the wire isa non-linear measure of stream velocity. The disadvantages of hot wireanemometry include its intrusive character and non-linear output. Hotwire anemometry also depends upon a measure of total heat transfer fromthe wire and not a measure of a predetermined amount of heat transfer.In other words, hot wire anemometry determines how much heat transferoccurs and does not measure the result of a heat transfer, i.e.,temperature change.

A publication entitled "Analog Devices, Multiplier Application Guide,"by James Williams et al of Analog Devices, Inc. (1978), teaches athermally operated flow meter for measuring fluid flow rate. A length ofpipe is inserted into or connected to a line carrying the fluid. Thepipe includes a resistive heater and upstream and downstream intrusivetemperature measuring probes. This device is effective only formeasurement of very slow flow rates and requires complex circuitry toenable a constant amount of heat to be supplied to the fluid stream. Thedevice further includes screens located in the pipe or elsewhere in theflow stream to mix the fluid and enhance temperature measurementaccuracy.

Flow meters which operate on thermal principles, such as the device inthe Poppendiek et al patent, are adapted only for measuring the flowrate of a fluid and are not capable of measuring an amount of heat addedto or extracted from a fluid by an unknown heat source or heat sink.

SUMMARY OF THE INVENTION

The present invention provides a non-intrusive heat monitor and methodto measure the thermal energy or thermal power input or withdrawal froma flowing fluid in a relatively inexpensive, efficient, and easy manner.More specifically, the present invention provides a non-intrusiveapparatus and method which measures the amount of thermal powerwithdrawn from or added to a flowing fluid by using a determinedsensible heat capacity rate of the fluid stream.

The monitor of the present invention includes a non-intrusive thermalpower transfer device capable of adding or removing a known ormeasurable amount of heat to a fluid stream flowing through a fluidcarrying conduit. The thermal power transfer device may be a heater, forexample, an electrically resistive heater. The heat transfer device maybe a heat sink, for example, a refrigerator system. While either can beused, the heater is often preferred. This power transfer device is areference thermal power transfer device because it determines areference signal. A first temperature differential sensing means adaptedto measure a first temperature differential across the thermal powertransfer device determines the temperature change in the fluid due tothe heat added to or removed from the fluid stream by the transferdevice. The first temperature differential sensing means includes a pairof non-intrusive temperature sensors for location across the thermalpower transfer device. A second temperature differential sensing meansof one or more temperature sensors senses the temperature across anunknown heat source or heat sink. The first temperature differentialtemperature sensing means, along with the reference power transferdevice, determines the heat capacity rate of the fluid in the flowingfluid stream.

The temperature measurements which give rise to the temperaturedifferentials are preferably converted in a converter to electricalsignals which are functions of the measured temperature differentials.More specifically, these electrical signals are proportional to themeasured temperature differential, although they do not have to belinearly proportional. They can be frequency or digital representationsof the measured temperature differential, or analog, and a function oftemperature. Means determine the heat capacity rate of the fluid in thefluid stream from the temperatures provided by the first temperaturedifferential means. Means multiply the temperature differentials acrossthe unknown sources or sinks by the determined heat capacity rate of thefluid. This results in a determination of the amount of heat (or thermalpower) which has been added to or withdrawn from the fluid stream by theone or more unknown heat sources or heat sinks. The result can be usedto control a function, as for example, control the unknown source orprovide control over the thermal reference device.

The direction of fluid flow with respect to the reference thermal powertransfer device and the one or more unknown heat sinks or heat sourcesis not critical to the invention, although temperature differentialsmust be taken in a consistent direction, for example, from upstream todownstream or downstream to upstream. The unknown heat sources orunknown heat sinks, if more than one, may be located on different sidesof the reference thermal power transfer device.

The monitor and method are primarily operable with a series fluidstream. That is, the thermal power transfer device, the unknown sourceor sink, and associated sensors operate on the same stream and not onparallel streams.

In a more detailed embodiment of the invention, the thermal powertransfer device is an electrically operable heater with a constantelectrical resistance so that the amount of heat generated isproportional to the square of the current or voltage used to providethis heat. In addition, the energy in the amount of heat applied to thefluid, with negligible loss, is substantially equal to the energy in theelectrical power consumed to generate that heat. This current, orvoltage, or electrical power provides a measure of the amount of heatapplied and is processed in a circuit to determine the heat capacityrate of the fluid in the fluid stream and also to enable measurement ofthe amount of heat added to or removed from the fluid stream by theunknown heat source or heat sink.

In a preferred form, the heater includes a heater element of alloy wirein a silicone sheet. This heater is jacketed in an insulation, say, ofsilicone foam. A sleeve encases the insulation and has means forattaching the entire unit to a pipe through which the fluid to bemonitored passes. Such attachment means might be in the form of hook andpile fastening strips. A radiation shield encapsulates the insulationsleeve. The temperature sensors are themselves insulated to avoidenvironmental influences. They are also attachable to the line as bysome fastener means such as hook and pile fasteners.

The temperature sensors should be fairly sensitive, preferably to withinabout 0.001 degrees Celsius to minimize necessary reference temperaturedifference to achieve system accuracy. It has been found that to avoideffects of heat conduction on the pipe and poor thermal mixing on theaccuracy of the instrument, it is desirable to observe a point ofattachment upstream and downstream of the thermal power transfer deviceof at least 10 and preferably 20 pipe diameters for the temperaturesensors. This spacing criteria is especially desirable downstream fromthe reference heat transfer device. The same spacing is importantdownstream of the unknown thermal power sources or sinks unless it isknown that the fluid is well mixed at that point.

"Heat capacity rate" is the amount of energy added or withdrawn from astream per unit time per unit temperature change in the stream.

The term "heat contribution" or the term "thermal power contribution"refers to that amount of heat or thermal power which is either added toor removed from the fluid stream, the term "contribution" being used inboth a positive sense when thermal power is added and a negative sensewhen thermal power is withdrawn from the fluid stream.

These and other features, aspects and advantages of the presentinvention will become more apparent from the following description,appended claims and drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic block diagram illustrating one arrangement of athermal power monitor constructed in accordance with the presentinvention in relation to an unknown thermal power source or sink;

FIG. 2 is a schematic block diagram illustrating another arrangement ofa thermal power monitor constructed in accordance with the presentinvention in relation to an unknown thermal power source or sink usingdifferent temperature sensor arrangements;

FIG. 3 is a schematic block diagram illustrating another arrangement ofa thermal power monitor constructed in accordance with the presentinvention in relation to a plurality of unknown thermal power sources orsinks;

FIG. 4 illustrates somewhat schematically a preferred form of thethermal power monitor of the present invention;

FIG. 5 is a schematic electrical circuit for the invention embodiment ofFIG. 4; and

FIG. 6 is an alternate embodiment of an electrical circuit for providingtotalizing information.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1 illustrates in a simple schematic block diagram form a thermalpower monitor designated by reference letter "A" for monitoring anunknown thermal power sink or an unknown thermal power source,designated as TDU. Monitor "A" comprises a reference thermal powerdevice TDR. In the preferred form, the reference thermal power device isa heater which applies a known or measurable amount of heat to a fluidstream. However, a cooling device which withdraws a known or measurableamount of heat from the fluid stream can be employed as the referencethermal power device. In the specific embodiment shown in FIG. 1,thermal reference device TDR has an electrical resistive element 10 andand a power meter 12 connected to the resistiveelement for measuring theamount of electrical power delivered to element 10 and provides ameasure of the amount of heat supplied to a fluid stream.

In the embodiment illustrated in FIG. 1, a fluid stream is carried in aconduit 14. Thermal reference device TDR is disposed outside conduit 14in thermal communication with it. The thermal reference device does notintrude into the fluid stream.

Thermal power monitor "A" also utilizes a first temperature differentialmeasuring means including a first temperature sensor T-1 on one side ofthe thermal reference device TDR and a second temperature sensor T-2 onthe opposite side of the thermal reference device TDR, in the mannerillustrated. In this way, a first temperature differential across thetemperature reference device can be measured which is used to determinethe heat capacity rate of the fluid in the fluid stream, as describedbelow.

The thermal power monitor includes a second heat differential measuringmeans in the form of a third temperature sensor T-3 located on thedownstream side of heat sink or heat source TDU. The third temperaturesensor cooperates with the second temperature sensor T-2. Sensors T-2and T-3 are designed to measure the amount of heat added to or withdrawnfrom the fluid stream by the unknown source or unknown sink TDU.

For purposes of understanding the theory of operation, assume that thethermal reference device is a heater. If the rate of heat input, dQR,into the fluid across the thermal power device TDR is known ormeasurable, then the rate of heat input or the rate of heat withdrawal,dQU, across the unknown heat sink or heat source can be determined.

By measuring the temperature differential across reference thermal powerdevice TDR, it is possible to determine the heat capacity rate. Heatcapacity rate "C" is the amount of energy added or withdrawn from astream per unit time per unit temperature change in the stream, (forexample, Btu/hr/° F.). In essence the heater or other reference thermalpower device along with the temperature differential measured across itprovides a heat capacity rate of the fluid. The heat capacity rate isnumerically similar to, but in lieu of, a measurement of the mass flowrate of fluid multiplied by the specific heat of the fluid. Using heatcapacity rate, it is not necessary to know the specific heat of thefluid or its mass flow rate, although the specific heat and flow rateshould remain relatively constant during measurement. Small changes inthe specific heat of the fluid and the flow during a determination ofheat capacity rate will not adversely affect the result. Large changesin specific heat or flow rate will not affect the determination of heatcapacity so long as they occur over a time span longer than the timerequired for measurement. Inasmuch as all measurements are being made onan entire fluid stream, for example, on a single conduit, and no fluidis added or removed from the stream between the first and lasttemperature sensors, the specific heat and the flow rate of the fluidwill be the same at all points in the monitorial section of the stream.

The methodology is to divide the amount of thermal power introduced intothe stream, dQR, by the first temperature differential, (T2-T1). "dQR"may be the known or measurable amount of electric power which,obviously, is a function of voltage and current delivered to thermalpower device TDR. The quotient is the heat capacity rate C.

When the temperature differential (T3-T2) across the unknown heat sourceor unknown heat sink is obtained by the temperature sensors T-2 and T-3,the temperature differential is multiplied by the heat capacity rate todetermine the net thermal power which is added to or removed from thefluid stream in the conduit section between temperature sensors T-2 andT-3 by the unknown thermal device TDU. By knowing the heat capacity ofthe flowing fluid stream, when a particular temperature increase ortemperature decrease is determined across an unknown source or sink, itis possible to determine exactly how much heat is added or removed fromthe fluid stream.

If the temperature measurement at the first temperature sensor T-1 isT1, the temperature measured by the second temperature sensor T-2 is T2,and the third temperature measured by the third temperature sensor T-3is T3, then the thermal power contribution is represented by theequations:

(1) Determination of heat capacity rate is: ##EQU1## the specificembodiment where TDR is an electrical resistance heater; ##EQU2## whereP is the electrical power provided to the heater.

(2) Determination of thermal power contribution dQU is:

    dQU=C(T3-T2).

(3) In a combined form, means hereinafter described solves the equation:##EQU3##

Importantly, the monitor of this invention does not require knowledge offlow rate and the specific heat of the fluid. Further, it does notmatter if the fluid stream contains solid or particulate matter. It is,of course, desirable to have the fluid stream relatively homogeneous, atleast between the various temperature sensors during any particularthermal power contribution measurement, and the homogeneity changesshould be slower than the response time of the equipment. Amicroprocessor can be used to average out differences in the homogeneityof the matter in the fluid stream.

The temperature differences which may be used for efficient operationcan even be quite small, for example, on the order of 0.5 degrees C. Inmany cases the device may be operated with temperature differences onthe order of about 1 degree C.

It is also possible to measure other forms of energy or power which maybe added to or removed from the fluid stream. For example, the thermalpower monitor of the present invention can be used to measure the risein the internal energy of an adiabatic fluid stream which may result,for example, from a flow restriction causing a drop in the stream'spressure energy. This is effective for non-intrusive trouble-shooting offouled piping systems and the like. For example, it has been determinedthat a four atmosphere pressure drop (60.7 pounds per square inch) in astream of water will give rise to about 0.1° C. temperaturedifferential. It has also been found that the thermal power monitor ofthe present invention is able to determine temperature risescorresponding to pressure drops as low as 2.5 p.s.i. and of 10 to 60p.s.i. with fairly good accuracy.

FIGS. 2 and 3 illustrate alternate arrangements of a thermal powermonitor of the present invention with respect to one or more unknownthermal power sources or thermal power sinks. FIG. 2 illustrates analternate arrangement using first and second temperature sensors T-1 andT-2 across the thermal reference device TDR, but in this case a pair ofindependent temperature sensors T-3 and T-4 are located across unknownpower sink source or sink TDU.

FIG. 3 illustrates an embodiment in which two unknown thermal powersources or thermal power sinks, namely, TDU-1 and TDU-2, may be used formonitoring thermal power addition or thermal power extraction from afluid stream. In this case, first unknown thermal power source or sinkTDU-1 has the temperature differential across the fluid measured bytemperature sensors T-3 and T-4. The second unknown thermal power sourceor thermal power sink TDU-2 has the temperature differential across itmeasured by temperature sensors T-5 and T-6. Thus, it is possible todetermine the amount of thermal power added to or removed from thestream by each of these two unknown sources or sinks independently.Further, by determining the temperature differential between T-3 andT-6, it is possible to determine the overall thermal power contributionfrom both unknown sources or sinks. It is also possible to determine theentire contribution to or from the fluid stream including that providedby thermal reference device TDR by determining the temperaturedifferential from the sensor T-1 across the system to the temperaturesensor T-6 as the second temperature differential.

The unknown thermal power contribution, for example, the unknown thermalpower addition by each unknown source or sources, or the unknown thermalpower drain by each sink or sinks, or combinations thereof, in theembodiments illustrated in FIGS. 2 and 3, is determined in the samemanner as the embodiment of FIG. 1. In each case the pertinenttemperature differential is multiplied by the determined heat capacityrate.

FIG. 4 illustrates a more preferred embodiment of the thermal powermonitor of the present invention in which an unknown amount of thermalpower is added to or removed from the fluid stream in the conduit orline 14 by means of an unknown energy sink or energy source TDU. In thiscase, reference is made to the amount of thermal power as the actualphysical parameter which is measured by the monitor of the invention.Thermal energy added to or removed from the fluid stream may bedetermined by measuring the power over a specific time duration at aspecific power level.

In the embodiment of the invention illustrated in FIG. 4, the heatreference means or device TDR is a heater 15 which provides a knownamount of thermal power (heat) introduced into the fluid stream. Heater15 includes an inner sheath 16 of flexible, dielectric material thatimbeds alloy heating coils 18 supplied with electrical energy throughlines 20. Sheath 16 is preferably thin, flexible, and formed of adielectrical material, for example, it may be silicone based. It has aparting line 22 to permit its application to line 14.

An insulation jacket 24 encases the sheath and overlaps its ends. Thisjacket also is split and has a parting line 26. The insulation issufficient to avoid material heat loss to the environment, eitherradially of the heater or upstream or downstream of heater 15. Theinsulation assures that the heat energy from heater 15 is essentiallycompletely introduced into the fluid flowing through line 14 withintolerable bounds.

A flexible cover 28 encases insulation jacket 24 and includes means forsecurely attaching the heater to conduit 14. These means include hookand pile type fasteners. Specifically, a set of four mating hook andpile type fasteners 32, 34, 36 and 38 of the cover cooperate to securethe cover, insulation and heater sheath firmly to conduit 14. The outersurface of cover 28 has a radiation shield 29 of metal foil thatisolates the conduit 14 in the zone of the heater from environmentalradiation.

Three temperature sensing units are also used. The first of these isupstream of the heater and is indicated by reference numeral 40. Thisunit 40 includes insulation 42 and a temperature probe 44 adapted torest against a surface of the conduit 14. Hook and pile fasteners 46secure the insulation and probe to conduit 14. A downstream temperaturesensing unit 50 is of basically the same construction. It has atemperature probe 52 backed by insulation 54, the entire unit beingsecurable to conduit 14 by hook and pile fasteners 56. A thirdtemperature sensor is shown at 60 and it again includes a temperaturesensor probe 62 backed by insulation 64 and attachable to conduit 14through hook and pile fasteners 66.

A control console 70 (to be described in some detail subsequently)provides for the integration of the heat input or extraction informationwith the knowledge of the heat input or removal by unknown source orsink TDU. It may also contain amplifier, offset, and feedback circuitry,if required, to effect accurate temperature sensing.

Preferably, the heating sheath is of a silicone rubber material withso-called "Cupron" wire conductors. These "Cupron" wire conductors areformed of an alloy of aobut 45% nickel and 55% copper and offered by theAmax Specialty Metals Corp. (formerly Wilbert B. Driver Company) ofParsippany, N.J. The Cupron wire is designed to have a resistance of 15ohms and therefore a unit rating of 666 watts when used with a 100 voltpower source. This particular type of wire has an electrical resistancewhich is not very temperature sensitive, and thus has a substantiallyconstant electrical resistance over a wide temperature range. Thispermits an easy correlation of electrical power consumption and thermalpower transfer and a single electrical parameter, for example, currentor voltage supplied to the heater. The thinness of the silicone rubberand the flexibility of the wire allow the unit to make excellent thermalcontact with the line or conduit 14 when held in place by the insulationjacket and sleeve.

A thermal power meter constructed in accordance with the principles ofthis invention has an accuracy within plus or minus 3% over a wide rangeof flow rates and energy input rates from the unknown source. The unitis lightweight and obviously very easy to use. It is extremely versatilein that the unit can be strapped to various sized pipes in a matter of afew seconds. The insulation jacket is of simple design and can bemounted quickly merely by placing its halves over the pipe.

Accuracy of the system was determined to be only weakly dependent on themass flow rate of the fluid being monitored and more strongly related tothe energy or thermal power output or drain by the unknown source orsink.

The location of the temperature sensors on either side of the heatingunit affects the accuracy of the meter. The closer the sensors are tothe heater, the greater the effect the mass flow rate of the fluid hason meter accuracy. For example, in one test when the temperature sensorswere moved to a distance of six inches from the heater on a one-inchline it was found that the accuracy was only plus or minus 10%.

The thermal response time of the system is comparatively rapid. Itdepends upon flow rate and heater insulation. A temperature sensorbacked by a 11/4 inches thick insulation needs about 5 to 7 minutes toachieve 95% of the equilibrium temperature of the pipe. This lag timecan induce error. Response time can be reduced by improving the heattransfer from the fluid to the temperature sensors and by making themass and thickness and heat capacity of the sensors and the associatedinsulation small.

The temperature sensor position with respect to the heater was found tohave an effect on accuracy because of two conditions: (1) heatconduction up and down the line, and (2) poor thermal mixing downstreamin the heated fluid. These effects are greatest at low Reynolds numbers.It is found that for a horizontal line with a Reynolds number of 6,000,temperature sensor positions 20 diameters from the heater virtuallyeliminated these problems. A downstream deviation of about 3% occurredat a little less than 10 diameters. The upstream deviation is lesssensitive.

The insulation is important to avoid environmentally induced errors.Tests reveal that diurnal air temperatures and radiation variations havean effect on what the sensors detect as temperature. In one instance itwas found that one of the sensors in close proximity to the metal shallof the test stand experienced a 0.1° C. shift in temperature compared tothe other two sensors. This was due to the radiation and convective heatinput from the metal test stand to the sensor. It is preferable to avoidthis effect by utilizing radiation shields between the environment andthe sensors. The shield can be placed on the outside of the insulationand, for example, may take the form of metal foil.

Temperature sensing circuitry should have a high sensitivity and shouldbe well matched to reduce the amount of heat energy that is necessaryfor the heater to supply. Satisfactory sensitivity is within 0.001° C.,and can be met by probes manufactured by Analog Devices, having modelnumber AD-590, in conjunction with the electronic circuitry hereinafterdescribed. The probe downstream of the unknown source, or sink TDU,namely probe 62, and its associated circuitry would not have to be assensitive if the temperature rise between probe 52 and probe 62 is 5 to50 times as great as between probes 44 and 52. A sensitivity for thethird sensor and its associated circuitry of 0.01° C. is satisfactory toaccurately determine this large temperature differential.

With reference to FIG. 5, a line schematic of the electrical aspects ofone embodiment of the invention is presented. An upstream temperaturesensor 100, corresponding to sensor 44, is in circuit with a powersupply and an operational amplifier 102. Specifically, the sensor is incircuit with a negative side of the power source 104 and an input to theamplifier. The power supply must be accurately controlled to avoid linevoltage fluctuations that would affect the accuracy of the monitor. Theamplifier circuit itself is standard. It is used to convert the currentcontrolled signal from the sensor into an adjustable voltage signal. Itincludes a lead 106 from the sensor, a lead 108 from the positive sideof the power source, and a lead 110 from the negative side. An input tothe amplifier is connected to ground potential through a resistor 112. Acapacitor 114 is connected across the amplifier 102 as shown. The outputof the amplifier 102 goes through a line 116 to a line 118. A resistor120 is between the output of the amplifier and the negative side of thepower supply. The output of the amplifier is indicated at VT-1.

The gain of the amplifier circuit is adjusted in a feedback branchcircuit 122. The circuit includes a variable resistor 124 in series witha resistor 126 to the line 118. Variable resistor 130 from a voltageregulator 131 couples into the circuit of variable resistor 124 andresistor 126 where they join the signal input of amplifier 102 at line133. The voltage regulator may be at a potential of 2.5 volts. Thevoltage through the circuit of these variable resistors and resistors isalso adjustable by a potentiometer 132 between them and ground. Thispotentiometer is mounted on the outside of the cabinet containing thiselectronic circuitry so as to be easily adjusted externally. Both thecircuits with variable resistor 130 and potentiometer 132 control theoffset voltage produced by amplifier 102.

A scaling or voltage dividing circuit develops a voltage signal VT-0.01.This circuit consists very simply of a resistance 140 from the output ofamplifier 102 in series with a variable resistor 142 and ground. Thesignal is taken off at line 144 and may be one hundredth the strength ofthe signal VT-1.

The circuits for the other two sensors corresponding to the downstreamtemperature sensor from the heater and the downstream temperature sensorfrom the unknown energy source or sink are shown at reference numerals160 and 162 and are identical to the circuit described with reference tosensor 100 except that the circuit of sensor 160 does not have anexternal fine adjustment. The external fine adjustment for circuit 162is indicated at 163 and corresponds to potentiometer 132. Sensor 160corresponds to sensor 52 and sensor 162 corresponds to sensor 62.Because of the identity of the circuits for these sensors they will notbe further described except to note that the output of sensor 160 isVT-2 and VT-0.02, and the output of sensor 162 is VT-3 and VT-0.03.

A signal VT-S representing the difference between the temperature sensedat 162 and the temperature sensed by sensor 160 times an appropriatescale factor (k) which is dependent upon the known reference power inputto the fluid stream is scaled in a branch circuit 164. That circuitincludes a resistance 168 and a variable resistor 170 in series. Thescale signal representing the difference of these two temperatures comesoff at line 174 between resistance 168 and 170. This signal is apotential relative to ground of a value (VT-2)+k[(VT-3)-(VT-2)].

A rotary switch 180 couples the output of the sensors and theiramplifier scaling circuits to a digital voltmeter 182.

Digital voltmeter 182 has four variable voltage input portions whichcontrol the numeric indication on a liquid crystal display 183. Theseare: IN HI, IN LO, REF HI and REF LO. The number displayed on the liquidcrystal display is the numerical value of the ratio of the potentials(IN HI-IN LO)/(REF HI-REF LO). Rotary switch 180 applies the differentsignals to digital voltmeter inputs to produce the desired ratios,differences, and values. Six positions of the switch are indicated bynumerals 1 through 6. In a first position, VT-S goes to IN HI, VT-2 toIN LO and REF HI, while VT-1 goes to REF LO. Digital voltmeter 182 thendisplays [(VT-S)-(VT-2)]/[(VT-2)-(VT-1)], which equals k[(VT-3)-(VT-2)]/[(VT-2)-(VT-1)]. This signal is the actual thermalenergy rate (thermal power) into the fluid stream between sensors 160and 162 when the scale factor (k) has been appropriately determined byresistances 168 and 170.

For displaying temperature differences useful to finely adjust thedevice by potentiometers 163 and 132, second and third positions areused. In the second position [(VT-2)-(VT-3)]/1.00 is displayed, with the1.00 coming from circuit 185 where a variable resistor 186 is in serieswith a resistor 187 and a constant voltage, for example, a battery 188.The variable resistor 186 has its tap 190 adjusted for 1.00 volts abovethe potential at 189, the potential at REF LO. In the third position allis the same except VT-3 is switched to IN HI in the place of VT-2.

To make each of the three sensors read the same temperature, they areall put at the same temperature for ten minutes, then the secondposition is selected and variable resistor 132 adjusted until thedisplay reads zero; then the third position is selected, and variableresistor 163 is adjusted until the display reads zero.

The individual temperatures of sensors 100, 160, and 162 can bedisplayed by using switch positions 4, 5 and 6, respectively. In thesepositions VTO.01, VTO.02 and VTO.03 are switched into IN HI, ground toIN LO and 1.00 is put between REF HI and REF LO. Then the displayindicates the value of the signals VTO.01, VTO.02 and VTO.03,respectively.

The auxiliary circuitry associated with the digital voltmeter is usedfor its functioning, but it is completely standard and will not bedescribed further, except for the filter produced by the connection of acapacitor 197 and a resistor 195 in parallel between the COM port on thedigital voltmeter and IN LO. This filter reduces instabilities found onswitch positions 1, 2 and 3.

The thermal power monitor can be made to totalize the amount of sensibleheat energy which flows into the fluid stream by using, in series, ananalog arithmetic division circuit to produce the[(VT-S)-(VT-2)]/[(VT-2)-(VT-1)] signal, then a voltage-to-frequencyconverter to produce a pulse train whose frequency is a direct andadjustable function of its input voltage, and finally a pulse countingcircuit to record each pulse. This is equivalent to recording each unitof energy which flows into or out of the fluid stream between sensors162 and 160.

The system could obviously be easily modified to include its referencepower input into its total power indication, by switching the connectionat 164 (to VT-2) on to VT-1 at 118, and also changing the IN LO signalwhen on position 1 of the rotary switch to VT-1 from VT-2. Then thedisplay would be k[(VT-3)-(VT-2)]/[(VT-2)-(VT-1)]+k ideally, whichequals the displayed k [(VT-3)-(VT-1)]/[(VT-2)-(VT-1)]. For example,this modification is effective when using embodiments as illustrated anddescribed in connection with FIGS. 1, 2 and 3. Thus, this modificationshows the simplicity involved in looking at power contribution usingvarious sensor arrangements and arrangements of unknown sources andsinks.

FIG. 6 illustrates one embodiment of an electrical circuit which iscapable of providing total information with regard to thermal powercontribution from an unknown source or an unknown sink. In thisembodiment of the invention, the signals generated at each of the threetemperature sensors, T-1, T-2 and T-3 are amplified by respectiveamplifiers 200, 202 and 204 which receive the signals from the threesensors. A thermal reference device TDR, namely a heater, is powered bya line voltage L to operate a resistive element of the heater forgenerating heat.

The amplified signals from the three sensors are introduced intodifferential amplifiers 206 and 208, in the manner as illustrated, forpurposes of removing spurious noise from the amplified signals and toalso provide for common mode rejection. The output of the differentialamplifier 208, which effectively represents the differential temperaturesignal T3-T2, is introduced into a multiplier 210 which multiplies thissignal by the determined heat capacity rate C, as hereinafter describedin more detail. This heat capacity rate C is provided from the output ofa divider circuit 212. The divider circuit effectively receives thesignal from the output of the differential amplifier 206 and which is,in effect, the differential temperature signal T2-T1. Further, thisdifferential temperature signal T2-T1 is divided into the square of theline voltage L which is also multiplied by a constant k representativeof the heater TDU and this output of the divider circuit 212 providesthe heat capacity rate constant C.

The output of the multiplier circuit 210 is introduced into avoltage-to-frequency converter 216 which converts the output to afrequency form capable of operating a totalizer 218 for thereupondisplaying the total thermal power contribution.

It is also possible to obtain an instantaneous display of thisinformation by means of a conventional display member 220. Outputs ofboth the differential amplifiers 206 and 208, as well as the individualamplifiers 200, 202, and 204 are introduced into a display selectcircuit 222, and the display select circuit 222 has an output forcontrolling the display member 220 in the manner as illustrated. In thecircuit of FIG. 6, differential amplifier 208 preferably may have aunity gain, and amplifier 206 may have a gain in the range of about 15to 20. The gains of the amplifiers are adapted to scale the outputsignals to the desired operating ranges of the multiplier 210 andmultiplier-divider 212. Multiplier 210 and the multiplier-dividercircuit 212, together with the voltage-to-frequency converter 216 andthe totalizer 218, integrate the time rate of the rate of the netthermal energy contribution in order to provide a total amount ofthermal energy contribution that is the amount of thermal energy eitheradded to or removed from the fluid stream.

This invention provides a unique and novel non-intrusive thermal powertransfer apparatus and method which permits determination of heat lossor heat gain with respect to a moving fluid stream.

The present invention has been described with reference to certainpreferred embodiments. The spirit and scope of the appended claimsshould not, therefore, necessarily be limited to the foregoingdescription.

What is claimed is:
 1. An improved non-intrusive thermal power monitorfor determining thermal power contribution to a fluid stream from anunknown thermal power source or sink, the monitor comprising:(a) thermalpower reference device means adapted to add or remove a known amount ofheat to or from a fluid stream flowing through a fluid carrying conduitwithout intruding into the fluid or conduit; (b) first non-intrusivetemperature differential measuring means for measuring a firsttemperature differential across the power reference device andgenerating an electrical signal which is a function of the firsttemperature differential, the first non-intrusive temperaturedifferential measuring means including a first temperature sensor and asecond temperature sensor, each such temperature sensor having means topermit its attachment to the conduit at least ten conduit diameters fromthe thermal power reference device; (c) second non-intrusive temperaturedifferential measuring means for measuring a temperature differentialacross a portion of the fluid stream that contains an unknown thermalpower source that adds thermal power to the stream or an unknown thermalpower sink that extracts thermal power from the stream, the secondtemperature differential measuring means generating an electrical signalwhich is a function of the second temperature differential; (d) meansfor determining the heat capacity rate of the fluid from the firsttemperature differential signal and the known amount of heat; and (e)means for determining the thermal power introduced into or removed fromthe fluid by the unknown source or sink from the heat capacity rate andthe second temperature differential signal.
 2. The improvednon-intrusive thermal power monitor claimed in claim 1 wherein thethermal power reference device is a heater which adds a known amount ofheat to the fluid stream.
 3. The improved non-intrusive thermal powermonitor claimed in claim 1 wherein the monitor is constructed so thatfluid flows first through the power transfer device before flowingthrough the unknown power sink or unknown power source.
 4. The improvednon-intrusive thermal power monitor claimed in claim 2 wherein theheater is an electrically operable heater where the amount of heatapplied to the fluid is proportional to the amount of current, orvoltage, or electrical power used to provide such heat, and the current,or voltage, or electrical power provides a measure of the amount of heatapplied.
 5. The improved non-intrusive thermal power monitor claimed inclaim 1 wherein the monitor includes a third temperature differentialmeasuring means for measuring a third temperature differential acrossand obtaining a third electrical signal representative of thermal poweradded to or removed from the fluid stream by means of a second unknownthermal power source or sink, and the thermal power determining meansreceives the third electrical signal and determines the thermal powercontribution to or from the fluid stream by the second unknown thermalpower source or sink.
 6. The improved non-intrusive thermal powermonitor of claim 2 including means for obtaining an electrical referencesignal from the known amount of heat and wherein the thermal powerdetermining means is adapted to divide the electrical reference signalby the electrical signal that is a function of the first temperaturedifferential.
 7. The improved non-intrusive thermal power monitorclaimed in claim 1 wherein the thermal power applied to or removed fromthe fluid by the unknown source or sink is acquired by multiplying theheat capacity rate by the signal that is a function of the secondtemperature differential.
 8. The improved non-intrusive thermal powermonitor claimed in claim 1 wherein the means for determining the thermalpower provides instantaneous measurements of thermal power contributionfrom the unknown source or sink.
 9. The improved non-intrusive thermalpower monitor claimed in claim 1 wherein the means for determining thethermal power provides a total measurement of thermal power contributionfrom the unknown source or sink on a time basis.
 10. A non-intrusivethermal power measuring apparatus for determining thermal power added toor taken from a fluid stream by a thermal power source or thermal powersink comprising:(a) reference heat application means for applying aknown amount of heat to a fluid passing through a fluid carrying conduitand for obtaining a signal representative of the known amount of heat;(b) a first temperature sensor for measuring a fluid temperature on oneside of the reference heat application means with respect to thedirection of fluid flow and generating a first electrical signal inresponse thereto and as a function of the measured temperature, thefirst temperature sensor including a probe and means on such probe topermit its attachment to the conduit at least ten conduit diametersupstream of the heat application means; (c) a second temperature sensorfor measuring the fluid temperature on the opposite side of the heatapplication means with respect to the direction of fluid flow andgenerating a second electrical signal in response thereto and as afunction of such measured temperature, the second temperature sensorincluding a probe and means on such probe to permit its attachment tothe conduit at least ten conduit diameters downstream of the heatapplication means; (d) a third temperature sensor for measuring fluidtemperature at the opposite side of said power source or thermal powersink with respect to either of the first or second temperature sensorsand generating an electrical signal representative of and a function ofthe temperature measured thereby; (e) thermal power determining meansincluding means for subtracting the first signal from the second signalto obtain a temperature differential signal, dividing the temperaturedifferential signal into the signal representative of the known amountof heat to derive a heat capacity rate of the fluid, using the thirdtemperature signal to obtain an unknown source or sink temperaturedifference signal, and multiplying that temperature difference signal bythe heat capacity rate to determine the thermal power contributionprovided by the unknown thermal power source or sink.
 11. Thenon-intrusive thermal power measuring apparatus claimed in claim 10wherein the thermal power determining means uses the second and thirdelectrical signals to determine a temperature difference across theunknown thermal power source or sink.
 12. The non-intrusive thermalpower measuring apparatus claimed in claim 10 including a fourth sensorlocated on an opposite side of the unknown source or sink with respectto the third sensor for providing a fourth electrical signalrepresentative of a temperature difference across the unknown source orsink.
 13. The non-intrusive thermal power measuring apparatus claimed inclaim 10 wherein the first temperature sensor is upstream of the heatapplication means, the second temperature sensor is downstream of theheat application means and upstream of the power source or power sink,and the third temperature sensor is downstream of the power source orpower sink.
 14. The non-intrusive thermal power apparatus claimed inclaim 10 wherein the heat application means is an electrically operableheater where the amount of heat applied to the fluid is proportional tothe amount of current, or voltage, or electrical power used to providesuch heat, and the current, or voltage, or electrical power provides themeasure of the amount of heat applied.
 15. The non-intrusive thermalpower apparatus claimed in claim 10 wherein the first, second and thirdtemperature sensors each have a temperature probe adapted to be attachedto the conduit and insulation surrounding a portion of each probe toisolate it from the environment.
 16. The non-intrusive thermal powerapparatus claimed in claim 10 including amplifier means for multiplyingthe signals from the temperature sensors.
 17. The apparatus claimed inclaim 10 or 11 wherein the third temperature sensor includes a probe andmeans on such probe to permit its attachment to the conduit at least tenconduit diameters from the power source or thermal power sink.
 18. Theapparatus of claim 10 wherein(a) the means on the probe of the firsttemperature sensor permits its attachment to the conduit at least twentyconduit diameters upstream of the heat application means; and (b) themeans on the probe of the second temperature sensor permits itsattachment to the conduit at least twenty conduit diameters downstreamfrom the heat application means.
 19. The apparatus claimed in claim 17wherein the sensitivity of the first and second temperature probes is atleast about 0.001° C.
 20. The apparatus claimed in claim 19 wherein thethird temperature sensor has a probe with a sensitivity of at leastabout 0.01° C.
 21. The apparatus claimed in claim 10 wherein theattachment means for the probes each includes a jacket of hook and pilefastener means and insulation means inside the jacket to isolate eachprobe from the environment.
 22. An improved, non-intrusive meter fordetermining the energy or power contribution to a fluid stream from asource or sink comprising:(a) a heater adapted for attachment to a linethrough which the fluid stream is passing, the heater including anelectrical heating element, insulation backing the heater element toprevent heat loss to the environment, and means for attaching the heaterto the line; (b) a first temperature sensor including a temperatureprobe adapted to be attached to the line upstream from the heater toobtain a first temperature signal, the first temperature sensor havinginsulation to isolate its probe from the environment; (c) a secondtemperature sensor including a temperature probe adapted to be attachedto the line downstream of the heater and upstream from the source orsink to obtain a second temperature signal, the second temperaturesensor having insulation to isolate its probe from the environment; (d)a third temperature sensor including a temperature probe adapted to beattached to the line downstream from the source or sink to obtain athird temperature signal, the third temperature probe having insulationto isolate its probe from the environment; (e) means for providing asignal representative of an amount of energy or power supplied by theheater to the stream; (f) means to obtain a first temperature differencesignal across the unknown source of the second and third temperaturesignals; (g) means to obtain a second temperature difference signalacross the heater of the first and second temperature signals; and (h)means for multiplying the energy or power signal by the firsttemperature difference signal across the unknown source or sink anddividing that product by the second temperature signal difference acrossthe heater to obtain the energy or power contribution or drain to thefluid stream from the source or sink.
 23. The improvement of claim 22including means to amplify the first, second and third signals.
 24. Theimprovement of claim 23 including means to amplify the differencebetween the first and second signals and means to amplify the differencebetween the second and third signals.
 25. The improvement of claim 22wherein the means for providing a signal representative of an amount ofenergy or power is the heater which is adapted to provide a constantamount of energy or power.
 26. The improvement of claim 22 wherein themeans for providing a signal representative of an amount of energy orpower is means for measuring the current or voltage or power applied tothe heater.
 27. The improvement claimed in claim 22 including:(a) meanson the first temperature probe to permit its attachment to the line atleast ten line diameters upstream of the heater; and (b) means on thesecond temperature probe to permit its attachment to the line at leastten line diameters downstream from the heater.
 28. A method fornon-intrusively measuring the amount of thermal power contribution to orfrom a fluid stream flowing in a conduit, the method comprising:(a)supplying or removing a known amount of heat to a flowing fluid streamby or from a reference heat means without intrusion into the fluidstream and obtaining a reference electrical signal thereof; (b)measuring a first temperature of the fluid stream at least ten conduitdiameters from the reference heat means without intrusion into the fluidstream and generating a first electrical signal in response thereto; (c)measuring a second temperature of the fluid stream without intrusioninto the fluid stream on the opposite side of the reference heat meansand at least ten conduit diameters from such heat means and generating asecond electrical signal in response thereto; (d) taking the differencebetween the first and second electrical signals to provide a temperaturedifferential signal across the reference heat means; (e) measuring athird temperature of the fluid stream with respect to an unknown thermalpower source which adds thermal power to the stream or an unknownthermal power sink which removes thermal power from the fluid stream andgenerating a third electrical signal in response thereto; (f)electrically determining the heat capacity rate from the temperaturedifferential signal and the reference signal of the amount of heatprovided by or removed by the reference heat means; and (g) determiningthe amount of thermal power added to or removed from the fluid stream bythe unknown source or sink using the third electrical signal and theheat capacity rate.
 29. The method of claim 28 wherein the firstelectrical signal is subtracted from the second electrical signal toprovide a temperature differential signal and this last namedtemperature differential signal is electrically divided into a signalrepresenting the heat applied to or removed from the fluid stream by thereference heat means to thereby determine the heat capacity rate. 30.The method of claim 29 wherein the third electrical signal is used withanother electrical signal to provide a signal representative of adifferential temperature measurement and this last named signal iselectrically multiplied by the heat capacity rate to determine theamount of thermal power added to or removed from the fluid stream by theunknown source or sink.